Method of controlling inking units in case of printing speed changes

ABSTRACT

A method controls a printing speed and a temperature of a printing press to attain a predetermined actuating variable. The printing press includes a control computer. The method is characterized by calculating a target temperature to attain the predetermined actuating variable at a desired printing speed and initiating the adjustment operations to attain the target temperature by the control computer. The actual printing speed is changed via a first acceleration within a tolerance limit with respect to fluctuations about the predetermined actuating variable. The first acceleration process is stopped if the desired printing speed is attained in the process. The first acceleration is changed if the tolerance limits are reached and the desired printing speed has not been attained yet. The printing speed is ran at a modified second acceleration along the tolerance limits until the desired printing speed is attained.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of Germanapplication DE 10 2011 109 360.9, filed Aug. 3, 2011; the priorapplication is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method of controlling the printingspeed and temperature of a printing press to attain a predeterminedactuating value, the printing press has a control computer.

In lithographic offset printing presses, ink is generally metered in theprinting unit by an inking unit that includes a number of ink zones.Each ink zone includes an ink key for adjusting the required openingsand thus the amount of ink. However, there are also inking unitsreferred to as short inking units, in particular anilox inking units,which do not include ink zones and ink keys for zonal metering.Therefore, in printing presses that have short inking units, the amountof ink cannot be metered by opening or closing zonal metering elements.Instead, other variables need to be influenced. A known fact is that inoffset presses, ink metering and thus the coloration of the printedproduct depends on the temperature and the printing speed of the press.Thus it is possible to use temperature changes and printing speedchanges to adjust the coloration in offset printing presses that have ananilox inking unit. In general, however, the press operator wants to seta certain printing speed to produce a desired number of printed productsin a specified time. Consequently, the desired target temperature forthe desired printing speed needs to be calculated and attained. Aproblem with adjusting the inking unit temperature is, however, that theinking unit only reacts sluggishly to temperature changes; it takes muchlonger to attain a desired temperature than to change the printingspeed.

The relationship between temperature and printing speed is known frompublished, non-prosecuted German patent application DE 102 54 501 A1,corresponding to U.S. Pat. Nos. 7,409,910, 7,261,034, 7,143,695,7,089,855, 7,021,215, and 7,004,070. In accordance with the method ofoperating a rotary printing press disclosed therein, the inking unittemperature is set as a function of the printing speed.

Published, non-prosecuted German patent application DE 10 2008 001 309A1, corresponding to U.S. Pat. No. 8,127,672, discloses a method that isintended to ensure that the ink density on the printed product remainsconstant by actuating printing speed and temperature in the inking unitin a matching way. The intention is to ensure that the dynamics of thespeed progression and the dynamics of the temperature progression arebetter matched with each other to attain a static ink curve relationshipeven for dynamic cases. Color measurement devices are known from U.S.Pat. No. 7,884,926 B2, U.S. Pat. No. 7,894,065 B2, and U.S. Pat. No.7,515,267 B2.

A problem of the prior art solutions is, however, that due to thesluggish temperature change, the printing speed can only be changed veryslowly to maintain approximately constant coloration. Another problem isthat the speed is changed in steps, resulting in a change of sign of thedriving forces, which has a negative effect on the printed image.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of controllingthe printing speed in short inking units in lithographic offset presseswherein quick speed changes are possible with as little effect on thecoloration as possible.

The method of the invention is particularly suited for actuation inoffset printing presses that include anilox inking units without zonalink metering devices. However, the method may likewise be used forprinting presses that have zonal inking units. The process implementedupon a printing speed change is carried out in a fully automatic way bya control computer that also controls the temperature in the press. Thedesired actuating variable is preferably the desired or targetcoloration. However, the desired actuating variable may also be anotheractuating variable of the press that is dependent on the temperature.The temperature itself may also be the actuating variable. All theseactuating variables that are dependent on the temperature are subject tothe problem that temperature changes develop very slowly, causingtemperature-dependent variables to quickly influence the condition ofthe press. This particularly applies to setting the desired targetcoloration to produce printed products in the press that have the samecolors as the original. In accordance with the present invention, thecontrol computer calculates the required target temperature that isnecessary to attain the predetermined actuating variable at a desiredprinting speed. Thus a suitable target temperature is calculated for thedesired colors and the desired printing speed in the inking unit of theprinting press. Then the control computer initiates the requiredactuating processes in the press to get from the actual value of theactuating variable to the calculated target value of the actuatingvariable. When adjusting the desired coloration, measures need be takento ensure that color changes are invisible or just tolerable to avoidthe production of unsalable waste during an adjusting process. For thispurpose, appropriate tolerance limits are stored in the control computerof the press. Until these tolerance limits are reached, the press cancontinue to run at the maximum acceleration. If the desired printingspeed is attained during this acceleration, the acceleration process isstopped and the printing operation is continued at the desired printingspeed that has been attained. If, however, the tolerance limits arereached before the desired printing speed is attained, the amount of theacceleration is reduced to an amount that does not cause change to theactuating variable, in particular the target coloration, within thetolerances. The printing press will then be accelerated to the desiredspeed along the tolerance limits until the desired printing speed isreached.

A great advantage of this method is that the desired printing speed isreached as quickly as possible by applying the maximum possibleacceleration while ensuring that the desired actuating variable remainswithin acceptable tolerances, i.e. for instance without deviating fromthe desired target coloration. Thus a speed change does not create anyspoilt products. The target coloration is preferably a desired inkdensity provided by prepress department based on the digital original.

In accordance with one embodiment of the invention, properties of thepress, properties of the ink to be used and properties of the printingmaterial are taken into account by the control computer in thecalculation of the acceleration and the desired printing speed.Factoring in the properties of the ink such as its tackiness andviscosity is an important aspect for the adjustment of the targetcoloration in particular. The properties of the press such as itssensitivity to temperature likewise need to be considered. Temperaturethresholds for the definition of tolerances in particular depend on theproperties of the ink, of the press, and of the printing material.

In accordance with a further embodiment of the invention, the respectiveacceleration may be constant. Alternatively, provision may be made forthe acceleration to be changed in steps by the control computer. In theconstant-acceleration embodiment, the press is initially accelerated atmaximum acceleration up to the tolerance limit and is then acceleratedalong the tolerance limit at the maximum possible acceleration. In bothcases, the acceleration is constant. In accordance with an alternativeembodiment of the invention, the control computer calculatesacceleration steps and the press is accelerated in steps within thetolerances, with tolerance limits being the upper limits of theacceleration steps so that the acceleration steps are not outside theacceptable tolerance limits.

In accordance with a further embodiment of the invention, the tolerancesare selected in a way to create color fluctuations that are just withintolerable limits. This is an alternative to the selection of tolerancelimits that do not result in any visible color fluctuations when theyare reached. In some printed products that do not require top printingquality, slight visible color fluctuations are acceptable. For suchjobs, it is possible to sell printed products that have acceptable colorfluctuations. Consequently, tolerances may be greater, the accelerationmay be increased, and the desired printing speed may be reached sooner.

In accordance with yet a further embodiment of the invention, during theadjusting process, a target acceleration may be defined as a function ofthe temperature of the press instead of target speeds. If the drivemotor of the press is actuated in this way, instead of respective targetspeeds, a torque for a target acceleration is defined and transmitted tothe drive motor during the acceleration process and the motor isoperated at this acceleration.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method for controlling inking units in case of printing speedchanges, it is nevertheless not intended to be limited to the detailsshown, since various modifications and structural changes may be madetherein without departing from the spirit of the invention and withinthe scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagrammatic, illustration of a sheet-fed rotarylithographic multicolor offset printing press including short inkingunits and a control computer according to the invention;

FIG. 2 is a graph for illustrating a speed compensation principle inoffset printing presses;

FIG. 3 is a graph for illustrating a temperature progression over timeand associated temperature tolerance limits for coloration;

FIG. 4 is a graph for illustrating the relationship between printingspeed and temperature and the associated tolerance limits for thecoloration;

FIG. 5 is a graph for illustrating an increase of the printing speedfrom 6,000 to 12,000 sheets per hour with identical coloration;

FIG. 6 is a graph for illustrating a progression of the printing speedas a function of time when the printing speed is increased from 6,000 to12,000 sheets per hour with identical coloration;

FIG. 7 is a graph for illustrating the relationship between temperatureand printing speed when the printing speed is increased from 6,000 to8,000 sheets per hour with identical coloration;

FIG. 8 is a graph for illustrating the progression of the speed as afunction of time when the printing speed is increased from 6,000 to8,000 sheets per hour with identical coloration;

FIG. 9 is a graph for illustrating an increase of the printing speedfrom 6,000 to 12,000 prints per hour with reduced coloration;

FIG. 10 is a graph for illustrating the speed progression as a functionof time when the printing speed is increased from 6,000 to 12,000 sheetsper hour with reduced coloration;

FIG. 11 is a graph for illustrating the relationship between temperatureand printing speed when the printing speed is increased from 6,000 to12,000 sheets per hour with increased coloration;

FIG. 12 is a graph for illustrating the relationship between printingspeed and time when the printing speed is increased from 6,000 to 12,000sheets per hour with increased coloration;

FIG. 13 is a graph for illustrating the progression of the printingspeed over time and the acceleration over time when the printing speedchanges from 10,000 to 18,000 sheets per hour;

FIG. 14 is a graph for illustrating speed and acceleration as a functionof time when the printing speed is increased from 10,000 to 12,000prints per hour; and

FIG. 15 is a graph for illustrating the progression of the temperatureas a function of time with a maximum acceptable temperature differenceof 6%.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is particularly suited for controlling colorationin zoneless lithographic offset printing presses 1 including shortanilox inking units 14. Such short anilox inking units 14 are used insheet-fed offset printing presses 1 as well as in web-fed rotaryprinting press in particular in the field of newspaper printing. By wayof example, FIG. 1 illustrates a four-color sheet-fed anilox offsetprinting press 1 including four printing units 2. In principle, allprinting units 2 are of similar construction: each includes a platecylinder 5 carrying a printing plate of the respective color separation,a blanket cylinder 4 for transferring the ink from the plate cylinder toprinting material 7 and an impression cylinder 3. The impressioncylinder 3 and the blanket cylinder 4 form a printing nip. Each printingunit 2 further includes an inking unit 14 embodied as a short aniloxinking unit. The inking units 14 generally consist of screen rollers andink applicator rollers. In addition, each printing unit 2 has atemperature control circuit 16 for separate adjustment of the printingink temperature in the individual inking units 14.

Like all other electrically adjustable machine components, thetemperature control circuits 16 are connected to a control computer 15.All printing units 2 are connected by a non-illustrated mechanical geartrain and are driven by a common drive motor 13. The sheet-shapedprinting material 7 is taken from a feeder 6 and fed to the firstprinting unit of the sheet-fed offset printing press 1. When the sheets7 have successively passed through the four printing units 2 to receivethe four color separations in the process colors black, cyan, magenta,and yellow, the printed sheets 7 are deposited in a delivery 11. Inaddition to being connected to the printing press 1, the controlcomputer 15 is also connected to a color measuring device 10 by acommunication link 8. Test sheets 7 taken from the delivery 11 can beplaced on the color measuring device 10 to be colorimetrically examined.The actual color values that are established in this way are transmittedto the control computer 15 by the communication link 8 and are comparedto the target values obtained from the prepress department based on theoriginal. If the control computer 15 detects unacceptable deviationsbetween actual color values and target color values, a colorationdifference that needs to be corrected is diagnosed. For this purpose,the control computer 15 calculates the temperature change required foreach inking unit 14 and the required speed change for a speedycompensation of the detected coloration differences.

To change the speed, the control computer 15 emits a correspondingcontrol signal to a drive motor 13 of the sheet-fed offset printingpress 1 via the communication line 8. Since the sheet-fed offsetprinting press 1 only has one drive motor 13, a speed change for thepurpose of changing coloration can only be implemented in all printingunits 2 at the same time. Changing the temperature offers more optionsbecause every printing unit 2 has its own temperature control circuit 16that can be individually actuated by the control computer. Thus eachanilox inking unit 14 can be heated or cooled separately as needed. Thepress 1 is operated using a screen 12 embodied as a touch screen,disposed on a control console 9, and is connected to the controlcomputer 15. If desired, the operator of the press 1 may make colorationchanges by hand using the touch screen 12.

FIG. 2 illustrates a desired target temperature T_(Soll) in percent independence on the printing speed V in sheets/hour. The temperatureT_(Soll) is given in percent of a minimum temperature and to a maximumtemperature. In FIG. 2, the temperature T_(Soll) associated with aconstant printing speed V corresponds to a desired coloration in percenton a printed sheet 7. FIG. 2 shows that a desired target coloration of30% of the maximum coloration at a printing speed V=3,000 sheets/hourcorresponds to a target temperature of 20%. For a printing speed V=6,000sheets/hour and a desired target coloration of 30% the targettemperature is 25%, for a printing speed V=9,000 sheets/hour and atarget coloration of 30% the target temperature is 30%, for a printingspeed V=12,000 sheets/hour and a coloration of 30% the targettemperature is 35% and at a speed V=15,000 sheets/hour and a 30%coloration the target temperature is 40%. The line above this line inFIG. 2 represents the relationship between the target temperature T andthe printing speed V for a coloration of 70%. In this case, the targettemperature for a printing speed V=3,000 sheets/hour is 60%. At a speedV=15,000 sheets/hour, the line intersects a target temperature value of80%.

For each target temperature T_(soll) there are temperature thresholdsbelow which no visible color fluctuations will occur if the printingspeed changes and temperature thresholds below which color fluctuationsare just tolerable though visible. The two thresholds may be determinedby experimental printing or by model calculations. The temperaturethresholds are ink-dependent and material-dependent; however, they maybe given as a mean value for one class of inks and materials.

The central graph of FIG. 3 represents the progression of the desiredtemperature T_(Soll). Above and below this graph, tolerance limits areindicated. These limits correspond to the values T+dT and T−dT, whichare the upper and the lower temperature limit, respectively, thatindicate coloration changes that are just acceptable. In FIG. 3, dT isassumed to be 5%. The printing press 1 is started up in such a way thatthe printing speed V is changed in a way to ensure that the temperatureT_(Soll) stays within temperature limits T+dT and T−dT. The deviation dTis calculated in the control computer 15 based on the target temperatureT_(Soll) and on the target printing speed V_(Soll).

FIG. 4 illustrates the development of the 30% coloration line independence on the printing speed V, the set temperature value T in % andthe upper and lower limits T_(PLUS) and T_(MINUS). The following speedchange rules are derived from these temperature limits: if the targetprinting speed V_(Soll) is between the acceptable limits V_(min) andV_(max), which are associated with the temperature limits T_(PLUS) andT_(MINUS), the printing press 1 may immediately be accelerated to thetarget printing speed V_(Soll). If the current printing speed V_(lst) isbelow the upper limit V_(max), which is in turn below the targetprinting speed V_(Soll), the printing press will initially beaccelerated to V_(max) and then slowly to V_(Soll). If both the actualprinting speed V_(lst) and the desired printing speed V_(Soll) are abovespeed V_(max), the current printing speed V_(lst) is maintained untilthe coloration is within the tolerances again.

If the current printing speed V_(lst) is greater than V_(min) andgreater than V_(Soll), the press is decelerated to printing speedV_(min). If printing speed V_(min) is greater than V_(lst) and greaterthan V_(Soll), printing speed V_(lst) is maintained in the press untilthe coloration is within the tolerances again. When all these settingsare completed, if required, the respective printing speed V is slowlyaccelerated towards the target speed V_(Soll) within the temperaturelimits and the speed limits as a function of the temperature T. As aresult, the printing press 1 reaches the target speed V_(Soll) asquickly as possible with the color deviations remaining within thetolerances. The actual speed V_(lst) is maintained as long as it takesfor the temperature T_(lst) to reach a level that permits furtherprinting speed changes towards the target speed V_(Soll). As analternative to such a slow continuous change of the printing speed V,the printing speed V may be changed in steps, for example in steps of1,000 sheets/hour. Another alternative is to accelerate more slowly fromthe start. However, this would prolong the dynamic condition.

In FIG. 5, a first exemplary development of the temperature T in % isshown as a function of the printing speed V, which is increased from6,000 sheets/hour to 12,000 sheets/hour. In the process, the targetcoloration value is to remain unchanged at 30% from the beginning to theend. The initial temperature at V_(lst)=6,000 sheets/hour isT_(lst)=25%, and the temperature tolerance limits are 5%. This meansthat the lower temperature limit T_(minus) is 20%, which corresponds toa speed V=3,000 sheets/hour at an identical coloration of 30%. The uppertemperature limit T_(plus) accordingly is 30%, which corresponds to atarget speed V_(Soll)=9,000 sheets/hour at a 30% coloration. This meansthat the minimum acceptable speed V_(min) is 3,000 sheets/hour and themaximum acceptable speed is V_(max)=9,000 sheets/hour. The actual speedV_(lst) is 6,000 sheets/hour, the target speed V_(Soll) is 12,000sheets/hour. Thus the control computer 15 may immediately accelerate theprinting press 1 to V=9,000 sheets/hour and then more slowly along thetolerance limit T=30% to V=12,000 sheets/hour. When the target speedV_(Soll)=12,000 sheets/hour is reached, the inking unit 14 continues tobe heated up by the temperature control circuit 16 to the optimumtemperature T of 35% for a speed V=12,000 sheets/hour.

FIG. 6 illustrates the progression of the speed V_(lst) as a function ofthe time t when the press 1 is accelerated from 6,000 to 12,000sheets/hour. The chart shows that initially, the printing press 1accelerates very quickly to 9,000 sheets/hour. Then it accelerates moreslowly along the tolerance limit at a second acceleration to a speed of12,000 sheets/hour.

FIG. 7 illustrates a second example, in which the printing press 1 isaccelerated from a printing speed V_(lst)=6,000 sheets/hour to a speedV_(Soll)=8,000 sheets/hour. Again, the target coloration ispredetermined at 30%, temperature T_(lst) is 25% at the speed V_(lst),and the temperature tolerance limit is 5%. This means that the lowerlimit T_(minus) is 20% and thus V_(min) is 3,000 sheets/hour. The upperlimit T_(plus) is 30%, which corresponds to a maximum speed V_(max) of9,000 sheets/hour. Since the target speed V_(Soll)=8,000 sheets/hour isbelow the maximum speed V_(max)=9,000, the printing press 1 mayimmediately be accelerated to the target speed V_(Soll)=8,000sheets/hour. When V_(Soll)=8,000 sheets/hour is reached, the inking unit14 continues to be heated up until the target temperature T_(Soll)=28,5% is reached. FIG. 8 again illustrates the progression of the speed Vas a function the time t. As can be seen, the printing press 1 mayimmediately be accelerated from 6,000 sheets/hour to 8,000 sheets/hourin one step.

A further example of a speed change is shown in FIG. 9. In FIG. 9, theprinting speed V_(lst)=6,000 sheets/hour is to be increased toV_(Soll)=12,000 sheets/hour. At V_(lst)=6,000 sheets/hour, the actualcoloration value is 30%. This value is to be reduced to 25% at a targetspeed V_(Soll) of 12,000 sheets/hour. At a target coloration of 30%, thetemperature T_(lst) is 25%; again the tolerance limits are 5%. Theprogression illustrated in FIG. 9 shows that the lower limitT_(minus)=20% leads to V_(min)=6,000 sheets/hour at the targetcoloration of 25%. The upper limit T_(plus)=30% corresponds toV_(max)=12,000 sheets/hour at a target coloration of 25%. This meansthat V_(max)=V_(Soll)=12,000 sheets/hour. Thus again in this example thepress 1 can immediately be accelerated to V=12,000 sheets/hour. Due tothe target coloration change to a lower value, the present case permitsan acceleration in a single quick step even through the printing speed Vis doubled. When the target speed V_(Soll)=12,000 sheets/hour isreached, the inking unit 14 continues to be heated up until atemperature T=30% is reached.

FIG. 11 illustrates a further example of a speed change. Again, theprinting speed is to be increased from V_(lst)=6,000 sheets/hour toV_(Soll)=12,000 sheets/hour. At V_(lst)=6,000 sheets/hour the targetcoloration is 30%, at V_(Soll)=12,000 sheets/hour, however, the targetcoloration is 40%. Again, at V_(lst)=6,000 sheets/hour T_(lst) is 25%,the tolerance limit dT is 5%. FIG. 11 shows that V_(min) is zero at thelower tolerance limit T_(minus)=20% and at the target coloration of 40%.At the upper limit T_(plus)=30%, V_(max) is 3,000 sheets/hour. Thismeans that at first, the press 1 needs to remain at a speed V=6,000sheets/hour until the inking unit 14 has been heated up to a temperatureT=30%. Then the printing speed V is slowly increased along the tolerancelimits to accelerate the press 1 to a speed V=12,000 sheets/hour. WhenV_(Soll)=12,000 sheets/hour is reached, the printing press 1 again needsto be heated even further until a temperature T=T_(Soll)=45% is reached.The associated speed progression V(t) is shown in FIG. 12.

FIG. 13 illustrates the printing speed progression V(t) and theacceleration a(t) at a given constant acceleration a. FIG. 14illustrates the progression of the printing speed V(t) and of theacceleration a(t). It can be seen that to remain below the tolerancelimits, acceleration a needs to be changed when a printing speedV_(lst)=10,000 sheets/hour is reached. FIG. 15 illustrates theprogression of the temperature T, of the target temperature T(V) and ofthe temperature difference dT. The tolerance limit dT is shown to be at6%. This tolerance limit is respected each time the temperature T ischanged.

The invention claimed is:
 1. A method of controlling a printing speedand a temperature of a printing press to attain a predeterminedactuating variable, the printing press having a control computer, whichcomprises the steps of: calculating a target temperature to attain thepredetermined actuating variable at a desired printing speed; initiatingadjusting operations to attain the target temperature by means of thecontrol computer, the adjusting operations including: changing an actualprinting speed via a first acceleration within tolerance limits relatingto fluctuations about the predetermined actuating variable; stopping thefirst acceleration if the desired printing speed is reached; changingthe first acceleration if a tolerance limit is reached and the desiredprinting speed has not yet been attained; and running the printing speedalong the tolerance limits at a modified second acceleration until thedesired printing speed is reached.
 2. The method according to claim 1,which further comprises calculating the modified second acceleration independence on a current deviation of an actual value from thepredetermined actuating variable.
 3. The method according to claim 2,which further comprises continuously adapting the modified secondacceleration to a difference between the actual value and thepredetermined actuating variable.
 4. The method according to claim 1,wherein if the tolerance limits have already been exceeded at a start ofa printing speed change, a printing speed is initially maintained by thecontrol computer until the tolerance limits are met again, and aprinting speed change is not implemented until then.
 5. The methodaccording to claim 1, wherein the predetermined actuating variable is apredetermined target coloration and the fluctuations are colorationfluctuations.
 6. The method according to claim 5, which furthercomprises choosing the tolerance limits to ensure that when thetolerance limits are reached, there are just not yet any visiblecoloration fluctuations.
 7. The method according to claim 5, whichfurther comprises choosing the tolerance limits to ensure that onlycolor fluctuations occur that are just tolerable.
 8. The methodaccording to claim 1, which further comprises taking into accountcharacteristics of the printing press, characteristics of a usedprinting ink and of a printing material by the control computer whencalculating at least one of the first or second accelerations and thedesired printing speed.
 9. The method according to claim 1, wherein atleast one of the first acceleration or the modified second accelerationis constant.
 10. The method according to claim 1, wherein at least oneof the first acceleration or the modified second acceleration is changedin steps by the control computer.